is there any non obvious reason that Chlorine would go up?

[poolshrinker]

First year pool owner, I had a pretty good feel/system going. i was checking my water with the TC and pH test every other day, occasionally letting it go 3 days, and adding about 1 qt of 10% LC every 1-2 days depending on how sunny it was and how much we were swimming. I was consistently losing 1.5-2 ppm per day, and with this regimen consistently staying at 4-5 ppm TC.

3 days ago the TC was 3 and I added 2 quarts of LC because the weather was turning sunnier and warmer. Today I checked and the FC is 10.5!!! It’s never been above 6 before. We did get about 1-2 inches of rain this week.

I don’t knowingly add any other source of chlorine to the pool. No tabs or additives.

CYA has been 30, now it’s halfway between 20 and 30. I’m thinking of adding some more stabilizer but the drop from 30 shouldn’t have caused chlorine to go up, right?

 

[Mdragger88]

I have noticed that the oto is not that accurate- maybe you’re fc was actually higher than 3 when u added lc . At least it wasn’t wrong in the other direction
Its more of a “oh good i have chlorine!” Type test.

 

[mgtfp]

Did you use a different batch of chlorine? Maybe you got used to old chlorine and now got a fresh batch. Did you check the date code? CYA shouldn't interfere with the FC test. Did you use FAS-DPD?

 

[duraleigh]

Chalk it up to testing error and move forward. Chlorine CAN NOT go up unless you put in chlorine.....no exceptions.